The complement cascade has evolved as a surveillance system in the blood stream against pathogens. However, activated complement is a double-edged sword that has the potential to cause significant damage to host tissues. Therefore under normal conditions, complement activation is tightly controlled by a number of regulatory proteins. Defective function of such regulatory proteins causes complement-dependent tissue injury and pathology. Several human diseases have recently been linked to dysregulated alternative pathway (AP) complement activity. Among them, the dry form of age-related macular degeneration (AMD), a common eye disorder affecting millions of elderly Americans that can lead to complete loss of eyesight. Atypical hemolytic uremic syndrome (aHUS) is another genetic disease that is characterized by hemolysis, thrombotic microangiopathy and kidney failure. Both of these disorders are associated with mutations in a key AP complement regulator protein, factor H, leading to uncontrolled AP complement activation and inflammatory injury in the retina and the endothelium, respectively. These conditions are difficult to treat due to the lack of appropriate therapies at the present time. We hypothesize that the development of effective AP inhibitors would help to control complement activation, thereby reducing inflammation and the progression of pathology in these diseases. In this exploratory research project, we will take advantage of the recent crystallization and structural determination of key AP complement proteins and use this knowledge to aid in computer-based drug design. For this goal, we propose to use a combination of high throughput screening and in silico computer-aided molecule design to identify and develop small molecule inhibitors of the AP that could be further developed into therapeutic agents for AMD, aHUS and other AP complement-dependent inflammatory diseases. We will pursue two specific aims: Specific Aim 1. We will perform further functional and kinetic studies of an identified small molecule inhibitor of AP complement activation and determine its specific protein target(s). Specific Aim 2. We will use in silico high-throughput molecular screening and structure-based molecular design tools to develop more effective chemical inhibitors based on the identified inhibitor. Most therapeutic studies in the complement field are focused on biologicals (recombinant proteins, antibodies and blocking peptides). Our proposed experiments have the potential to produce a novel class of small molecule chemical inhibitors of AP complement activation. These small molecules are significantly easier to produce and do not have the same biological hazards as recombinant proteins, antibodies, etc., making them far ideal for the affordable treatment of a wide variety of patients and diseases. PUBLIC HEALTH RELEVANCE: Our research goal is to develop a novel class of small chemical inhibitors of the immune system. Such inhibitors would fill a critical absence in the current ability to prevent or treat auto-immune and inflammatory conditions and represent an important advance to human health.